feat: add referral network graph visualization page

Interactive Sigma.js + graphology graph with ForceAtlas2 web worker
layout, campaign/user node coloring, filters via nodeReducer pattern,
search highlighting, user/campaign detail side panels, and 4-locale
translations. Dependencies: sigma v3, graphology, graphology-layout-forceatlas2.

src/api/referralNetwork.ts

@@ -0,0 +1,31 @@
+import apiClient from './client';
+import type {
+  NetworkGraphData,
+  NetworkUserDetail,
+  NetworkCampaignDetail,
+  NetworkSearchResult,
+} from '@/types/referralNetwork';
+
+export const referralNetworkApi = {
+  getNetworkGraph: async (): Promise<NetworkGraphData> => {
+    const response = await apiClient.get('/cabinet/admin/referral-network/');
+    return response.data;
+  },
+
+  getUserDetail: async (userId: number): Promise<NetworkUserDetail> => {
+    const response = await apiClient.get(`/cabinet/admin/referral-network/user/${userId}`);
+    return response.data;
+  },
+
+  getCampaignDetail: async (campaignId: number): Promise<NetworkCampaignDetail> => {
+    const response = await apiClient.get(`/cabinet/admin/referral-network/campaign/${campaignId}`);
+    return response.data;
+  },
+
+  search: async (query: string): Promise<NetworkSearchResult> => {
+    const response = await apiClient.get('/cabinet/admin/referral-network/search', {
+      params: { q: query },
+    });
+    return response.data;
+  },
+};